Wind turbines, especially utility-scale wind turbines, may include a yaw braking system that holds the wind turbine pointed into the wind, or that otherwise provides a resistance or damping to rotation of the wind turbine. Similar to conventional braking systems, pads or the like (e.g., yaw pads) may be employed to engage with a mating surface of the wind turbine referred to as a slew ring, which may be made of steel or the like. In particular, many wind turbines utilize a gliding yaw bearing arrangement that allows a nacelle of the wind turbine to rotate about a wind tower in a smooth and controlled manner. The yaw bearings may absorb large static and dynamic loads and moments during the wind turbine operation, and are structurally configured to provide smooth rotational characteristics for the orientation of the nacelle under many weather conditions. To this end, the yaw bearings may include relatively robust braking systems and assemblies.
In particular, the yaw pads may be coupled to a movable piston to provide predetermined ranges of pressure when engaging a slew ring of a wind turbine. In some instances, the movable piston is part of a hydraulic piston assembly, e.g., in a caliper-type yaw brake with yaw pads that engage a slew ring on opposite surfaces thereof (essentially squeezing the slew ring between two yaw pads), or otherwise in an assembly where a hydraulic piston is activated to engage one or more surfaces of a slew ring. Hydraulic piston assemblies of caliper-type yaw brakes may include a housing with a chamber containing the movable piston, where movement of the piston is provided by a pressurized, hydraulic fluid (e.g., oil) that enters the chamber through a hydraulic port. Typically, the hydraulic piston assembly will include a single high-pressure seal around an interior circumference of the chamber to prevent or mitigate oil from entering a certain volume of the chamber from which it could leak. The hydraulic piston assembly may also include a single bleed-off port for disposing of oil that has entered a certain volume of the chamber. Thus, in some hydraulic piston assemblies, leak prevention is established by a single high-pressure seal and a single bleed-off port, where the last line of defense against a leak is a component of the hydraulic piston assembly that is not structurally configured to prevent such leaks—e.g., a scraper seal that is not designed to withstand pressure from hydraulic fluid, but instead is designed to exclude contamination from the assembly (i.e., a scraper seal is not designed to retain oil). In this manner, in existing hydraulic piston assemblies there is one seal designed to prevent contamination and one seal designed to prevent leaking, where this configuration often fails leading to leaks in the brake assemblies.
There remains a need for improved seals for hydraulic brakes, e.g., sealing techniques for use in caliper brakes featuring a hydraulic piston assembly for use in wind turbines.